Ultra-high voltage (UHV) metal-oxide-semiconductor (MOS) devices were typically fabricated with coplanar drain and source regions. A common problem observed in the UHV MOS devices is the difficulty in the improvement of breakdown voltages. This not only posts limitations to the application of the UHV MOS devices, but also adversely affects the reliability of the UHV MOS devices.
In one of the applications of the UHV MOS devices, UHV MOS devices are used to form a level shifter, which generates a high voltage. The high voltage may be provided to a high-side gate driver, which may operate at the voltage range between 0 to 600V, for example. Accordingly, the level shifter needs to generate a voltage as high as 600V by pushing up a low source voltage, for example, 5V. In this circuit, the breakdown voltage of the entire circuit not only depends on the breakdown voltage of individual UHV MOS devices, but also depends on the breakdown voltage of the interconnection structures for conducting the high voltages.